defaultsinjs.js

function foo(one, two, three) {
  one = one || "defaultvalue"; // assigns default value if one is falsy (null, undefined, 0, "0", false, etc.)
  two = two == null ? "defaultvalue" : two; // assigns default value if 'two' is not null or undefined (so you can pass things like 0 or false)
  three = three === undefined ? "defaultvalue" : three; // assigns default value if three is not undefined (so you can pass null)
}